Testing arrangement for finder switches in telephone systems



Patented May 25, 1948 TESTING ARRANGEMENT FOR FINDER SWITCHES IN TELEPHONE SYSTEMS John William McClew and Owen Avis Pearce, Liverpool, England, assignors to Automatic Electric Laboratories Inc., Chicago, 111., a corporation of Delaware Application December 8, 1944, Serial No. 567,224 In Great Britain February 18, 1944 9 Claims.

The present invention relates to finder switch arrangements suitable for use in telephone or like electrical signalling systems, and is more particularly concerned with improvements in arrangements by means of which a marked line can be connected to equipment of difierent classes all serving a number of such lines.

In private automatic exchange or private automatic branch exchange telephone systems of the line finder type a number of finder/connector links are usually provided and are allotted for use under control of one or more common equipments. Calling lines gain access to these socalled local links via the finder portions of the links which hunt for line markings having finder bank positions characteristic of the calling subscribers concerned. Subsequently, in response to dialled digits characteristic of local subscribers, the connector portions of the links effect local au tomatic connections. In response to certain other characteristic dialled digits, other finder switches may be started up to connect the calling subscrlbers concerned direct to special service links.

A typical special service link connection occurs where two private exchange boards are linked by a tie line. In this case a calling subscriber on one board wishing to gain access to a subscriber on the other board will first dial a characteristic prefix digit or digits in response to which the local link taken into use will cause the tie line link to connect itself over a finder switch with the calling party, the local link then being released for further common use. The tie line link on being switched through to the calling subscriber will cause a local link on the other board to connect with the distant end of the tie line and further dialled digits which will extend into the tie line link will be repeated to the distant local link to effect connection with the required party. Another example, which occurs particularly on private automatic branch exchange boards, is the association of a main exchange line link with a calling subscribers line.

With regard to the various finding conditions involved, a normal calling line marking will appear on the multipled local link finder switch test banks, while the line marking for subscribers requiring special services will also appear in this multiple unless the test conditions for the finder switches of each of the special services provided for are segregated from the normal calling line test conditions. This latter method is, however, not always desirable or even feasible owing to. the additional equipment required which will usually involve extra banks and wipers on the local link finder and connector switches.

If the other arrangement is adopted whereby the test conditions for more than one type of finding operation can appear together in the local link finder switch test bank multiple, the question of possible cross switching will naturally arise. Arrangements have already been proposed whereby test conditions for two differing types of findin operation may appear simultaneously in a common bank multiple without danger of cross switching of the finder switches concerned.

When test conditions for three differing types of finding operation are likely to arise however, it has hitherto been thought essential to ensure that only one type of finding operation can take place at a time, which necessarily introduces delay particularly at busy calling periods when it is at least desirable.

It is an important object of the present invention to provide arrangements permitting three differing types of finding operation to take place simultaneously under conditions of the abovementioned character without any risk of wrong connection resulting.

According to one feature of the invention, in a finder switch arrangement suitable for use in telephone or like signalling systems, the operation of a finder to connect with a marked one ofa group of lines is under control of a double-wound relay not operative on either winding alone, one winding of the relay being connected in the marking circuit to potential of one polarity while the other winding is connected to the switch wiper and to potential of opposite polarity whereby separate markings of either polarity may be used to control the simultaneous operation'oi other classes of finders having access to the same lines.

According to another feature of the invention, in a finder switch arrangement suitable foruse in telephone or like signalling systems and having similar finders of three different classes adapted to hunt simultaneously over a group of' lines for markings respectively characteristic of the class of finder, for the first class the marking comprises potential of one polarity applied over a wiper of a finder of the third class, for the second class the marking comprises potential of the other polarity also applied over a wiper of a finder of thethird class and for the third class the marking comprises potential of the one polarity applied through the winding of a double-wound relay which is not operative on either winding alone the other winding of the relay being connected markings respectively characteristic of the class:

of finder, the finders of two of the classes being set in operation in response to;a: suitableeignalz transmitted over a calling line to which connection has already been made by'a finder of the:

third class, the test banks of finders ofithezsaidi two classes are directly multipledfand: are connected to the test banks of finders of the third class over back contacts of the-line relays, or the r associated lines while marking 015 a; calling line f in the banks of the third class of finders is offected over front contacts of the said relays whereby marking potential applied to the test banks-.of finders oithethird: class is not effective in the test banksofi the, finders of the other two.

classes; Y

The invention'will: be. better.- understood v from the:iollowin description'or onemethod. orcarrying: it into ffect; reference being had to. the ac= panying. drawing which shows: a basic circuit" of the; test conditions which obtain on; a.P:.'A. X; or EA... B:.;X- board of the above-mentionedrtype. if two; special service finder: switches: happen: to be hunting" for" particular subscribers" lines. atv the sametime as a local linkfinderswitchv ishuntins for an ordinary calling. line;

In thecircuitsjtypical values for the test relaywindings andifor the various resistances are siren for general: guidance;

Hairline represent; certain: parts; of the local finder/connector links such as: the: local finderi connector links described in PatentiNo; 2 ,087,930; ranted July 27, 1937, todohnzI-IrVOss; andin these. links. IFS l;:3ESlrepresent the test wipers and banks. of. theiuniselector finder. switches ICSIi -3GSI representwipers and banks ofthe two-motion. connector: switches, while lXl;'-3X.|;r are contacts of switching relays: within thelinks, contacts; IXI and 2X]: beingshown operated condition; ContactsLZLI', 5Ll5and lllIJlare-marking contactsiofthe well: knowniline relaysof: three subscribers. which will be referred to as lines 2, 5,. and

Locali links; LL! and LL? are. assumed to have associated-themselves with subscribers Nos. 2 and orespectively, the line relays 0t which only. the contacts- 2Ll and: 513i are shown. andwhich will have. been released in response to the operation ofthe associated'cut-off relays (not shown) in well knowmanner responsive: to the connectionof: the local finder connector links thereto. The con nector switches in these links are moreover. ase

sumedi tolhave been 'setby: dialling to positions which would'i'cause' the. finder'switchv AESsof special. service link SALto-hunt-for subscriber No. 2 andj which would cause finderfswitchBFS of'speoial service link SB]: tohuntfor subscriber No. 5; The special: servicelinks: SAL and: SEE represent certain partsof two way trunk irduitsandassociatedfinder switches such as! those in the Voss Patent 2,087,930; While only one; special service link SAL is shown and only one special service linksBLis shownit-may -be understood that'there is-a group ofspecial 'servce-links suchas the link and another group 'of special service links such- 'as the linkSBL. Allotting equipment, which may '-be similar to the 'allottin'g equipment AE; is provided tor each group sothat an: idle link in '4 each special service group is preselected for operation in the well known manner.

As regards link LL3, this is assumed to be finding an ordinary calling subscriber No. 10, the line relaycontacts; lllLl of which will be operated as shown. As: is usual practice, the, finder switch in link LL3- is assumed to be operated under the control of allotting equipment AE which includes the allottingswitch AS, the wipers of which will cqnneet llpiwithjink LL3. In the allotting equip-' mentthe-usual test relay which is usually of similar chara'Qtereto-relays SA and SB has been replaced bya: shunt; field relay for reasons which win; be appreciated: later.

Reviewing the'operation of the link LL3 finder switchntheswitchmagnet 3PM will be operated irra. salt-interrupted circuit via its contacts 3FMC, lead l4, bank and wiper ASZ and contacts LTl to earth so that it will advance the switch wipers.

including the test wiper 3FSI in a counterclockwisejdirection as: shown. Wiper. 3E8. I: connects via: normal contacts 3Xl,;lead:l5;:and;banls w p Ass with the earthedir-ishthandiwindting of the shunt field' relay' LT; while} the; sube scriberNo. 10 line marking onthefinderswitch bank comprises resistance: battery via: the; leit.-- hand winding of; relay LT whichr extends via re'-= sistance .YG, lead- [2 which is preferablncorhmon to all the-Subscribers servedbythe finder switches. shown and operated linet relay contacts. l-GL I: on, to a characteristic:positionorrbank- 3-I3PS I-.-

When wiper 3FSI1- reaches the line: markin the two windings-of relayLTfare energised-in; series and under this condition relay HI? rapidly; operates; as verified: by experiment with-the rer" sistance' values. indicated; and opens. the switch magnet driving cirouitaticontacts LTL, At'jthe. same, contacts it", extends: earth: over wiper: and bank ASl to lead; l3so asin known. mannerr't'o: initiate the operation ofa switching. relay? (not shown) which; at its contacts-3X! switchesvthe test lead from wiper-3FSl through to-,wipen 30S! and at other contacts (notshownl-conneets. the calling line over other, finderr switch: banks and wipers through totheilink circuit:imreadinesofor the reception of dialled. digits; It-will: be?

understood: that: the. operation and; subsequent holding of the subscriberscut-oif relay is. efiected: over another bank and wiper oithofinderswitcih:

Owing totheshunt fieldi magnetic circuit 'of relay LT, thisrelay will only. operatewhenboth its windings are; simultaneously energised? in'a predetermined direction, and. hence it will; only operate in the circumstances described.

Considering now theoperation. of the finder switch AFSi in thespecial servicelink SAL which issearching for subscriber No". 2;.the'linerma'rking will comprise-an:earthpotential.which is an?- pliedto a characteristic.- position. in barlklAFSli via the lowresistance winding offthe test .relay SA in link SAL, connector'switchbank and wiper I08 I of the locallink; LL! contacts: IXL. finder switch bank and wiper; IFSTI anddinerelay coni tacts 2Ll. a r

When wiper AFSI reaches this.--marking, relay SA will rapidly operate in :series withthe .battemconnected resistance. YA. and at contacts. SA-L will. open, the, magnet. driving.- circuit. and will extend earth over. lead. Ill-to initiatethe switch ingjthroughofthe calling, line No.2 to. thelink. SAL in known manner. r

With regard ,to the. operation of. the; finder switch BFS in link SBhwhichis searching ion subscriber No. 5;.the1ine markingcin tlfisrinstance' will comprise a battery potential which is applied to bank BFSI via resistance YB, bank and wiper ZCSI in link LL2, contacts 2XL, wiper and bank 2FSI and contacts L1.

When wiper BFSI encounters this marking, relay SB will rapidly operate in series therewith and will function in similar manner to relay SA. By virtue of the low resistance of relay SB an immediate guard is placed on the outlet seized and the adjustment of the relay is moreover such that once it has operated, if another similar test relay connects itself in parallel it will continue to hold while the second relay will fail to operate.

Consideration will now be given to the possibilities of cross switching when two or three of the finder switches such as AFS, BFS and 3F'S of the differing kinds of links SAL, SBL and LL3 are searching simultaneously for subscribers Nos. 2, 5 and respectively.

With regard to possible cross switching between links SAL and SBL, if resistances YA and YB have values such as 400 ohms and 150 ohms respectively, relay SA is adapted to operate in series with 400 ohms, and relay SB is adapted to operate in series with 150 ohms and not to operate in series with 400 ohms. Link SAL can never switch in to the 150 ohm battery comprising the marking for subscriber No. 5, since as it is not connected to the wiper of its associated finder relay SA can never encounter such marking. Conversely, link SBL can never switch in to the 400 ohm battery connected to the link SAL finder switch wiper AFSI, since this constitutes a non-operate condition for relay SB.

Cross switching between either of the links SAL or SBL and local link LL3 is impossible since the subscriber No. 10 battery marking comprising the 11 ohm battery-connected winding of relay LT in series with the 120 ohm resistance YC can never be encountered by either relay SA or SB. Thus as regards link SAL the finder switch wiper IFSI of local link LLI through which the test relay SA is connected up will be stationary and positioned as shown where it connects with the calling line relay contacts 2Ll of subscriber No. 2, and hence relay SA can never meet subscriber No. 10 marking, while as regards link SBL the subscriber No. 10 marking is prevented from extending to the BFSI bank by virtue of the respective connections to the back and front contacts lllLl of the line relay.

As regards the local link LL3, this cannot possibly switch in to the marking of either of the special service calling subscribers Nos. 2 and 5, since as previously mentioned the test relay LT will only operate when both its windings are energised in series.

Hence in the above-described manner as many as three differing types of links can simultaneously hunt ,for the appropriate lines in the same group and each is assured of switching in only to a specific line circuit.

What we claim as new and desire and secure by Letters Patent is:

1. In a telephone system, a line, a finder switch having a bank and a movable wiper therefor, a double wound shunt field relay for controlling the movement of said wiper, said relay being operative only in response to the energization of both of its windings, a marking contact for said line in said bank. means for energizing both of said windings upon the engagement of said wiper with said marking contact to operate said shunt field relay thereby stopping the movement of said wiper.

2. In a telephone-system having a plurality of lines, a finder switch having a wiper, marking contacts for said lines accessible to said finder, a double wound relay operative only in response to theenergization of both of its windings, means: for connecting a potential of one polarity through one winding of said relay to the marking contact of an individual one of said lines, means for connecting a potential of opposite polarity through the other winding of said relay to said wiper, said relay operative upon the engagement of said wiper and said last marking contact to control the movement of said finder.

3. In a telephone system having a plurality of lines, a first group of finders, a second group of finders, a third group of finders, marking terminals for said lines in each of said three groups of finders, means for applying a potential of one polarity to the marking terminals of any one of said lines for stopping the movement of one of the finders of said first group,'means for applying a potential of the opposite polarity to the marking terminals of any one of said lines for stopping the movement of one or" the finders of said second group, a double wound shunt field relay operable only in response to the energization of both of its windings, means for connecting the marking terminals in said third group of finders for any one of said lines to a potential of said opposite polarity through one of the windings of said relay, means for connecting a potential of said one polarity to a wiper of one finder of said third group of finders through the other winding of said relay, said relay operative upon the engagement of said wiper with one of said last marked terminals to stop the movement of said one finder of said third group, means for permitting simultaneous operation of finders in each of said groups, and means for stopping a finder of any one of said groups only in response to a marking for that group.

4. In a signalling system, a group of finderconnector links, switching contacts and a wiper in each link, a first group of finders, a second group of finders, a plurality of lines, marking terminals for said lines accessible to the finders of said links and accessible to the finders of said two groups, means for establishing markings of three different classes and for connecting said markings to different ones of said marking terminals, one of said classes of markings effective for stopping finders of said first group on marking terminals to which said one class of marking is connected, another of said classes of markings efiective for stopping finders of said second group on marking terminals to which said other class of marking is connected, and the last of said classes of markings efiective for stopping finders of said links on marking terminals to which said last class of marking is connected, means for permitting simultaneous searching by finders of said links and by finders of said two groups, means including the switching contacts and'the wiper of one of said links for stopping the finder of said one link only on a terminal marked for said group of finder-connector links, means including the switching contacts and the wiper in another of said links for stopping one of said first group of finders only on a terminal marked for said first group, and means including the switching contacts and the wiper of a further one of said links for stopping one of said second group of finders only on a terminal marked for said second group.

5. In a telephone system wherein similar finders :of three different classes have access to the marking contacts era plurality of lines, means portion cisaid marking contacts, -a source of potential having terminals of two polarities,

wipers on said finders, means for connecting a distinctive marking for one of said-classes otfinders to -marking contacts of-any one of said lines over'awiper of one of thefin-ders of another of said classes, said marking including potentialof one of said polarities, means forconnecting another distinctive lmarking-rfora further one of said-classes of finders to marking contacts for-any one of said li-nes'over the wiper of another finder-of-saidother class, said other distinctive marking including potential of the other of sai'dpol-aritiesa double Wound relay operative only in response tothe energization of both of its windings,-means for connecting a further .distinctive-marking-for said. other class of finders to marking contacts of any one of said lines, said-further marking including potential of said one-polarity-and one winding of said relay, and

tothe engagement of said last wiper with one of said last marked contacts.

6 In a switching system wherein the wipers of similar finders of three different classes hunt simultaneously over marking contacts fora plurality'of lines,,means for connecting a characteristimmarking :to a marking contact of one of said 'lines to control the movement only of a finder of one ofsaid classes, said means includinga wiper of a finder of another one of said classes, means .for connecting a different characteristic-marking to a marking contact of another of said lines to control themovement only of a finderof a further one-of said classes, said -means including a wiper of another finder of said 'otherclass, means for connecting a still diflferent characteristic marking to a marking contact of a'further one .ofsaid lines to control the movementonly of a-finder of said other class.

7. In asignalling system, finders of three different classes, a plurality of lines having test terminals accessible to each of said finders, wipers on said finders, means for permitting the wipers of finders of said three classes to hunt simultaneously over said test terminals, a source of 1 potential I having two polarities, characteristic 'markings of three different classes, means for connecting a characteristic marking of one of saidclasses to test terminalsof one of said lines over a wiper of a finder of one of said classes, said-marking including potential of one of said polarities, meansresponsive to said marking for stopping only afinderof another of said classes on a test terminal of said-one line, means for connecting another characteristic marking of another of said classes to test terminals of another one of said lines over a wiper of another 5 finder of said oneclass, said other marking including potential of the other'of .said polarities, .meansiresponsivefto said other marking for stoppingonly of a finderrof a-iurther-one-refsaid classes on-atest terminal-of said other lina -a double wound relay operative only in-response to the-energization of both of its windings,-means 'for connecting acharacteristic marking of a inrther one of saidclasses to test terminals of a further one of said lines, said lastmarking including 1 one winding of said relay and potential of saidotherpolarity, means for vconnectingepo- V group, the individual marking contacts of any one of said linesoperablein one manner'to connect the test terminals of said, line in only one of saidfinder groups to the characterist-icmarking for the same, thereby stopping the movement only of a finderin said one group on a test terminal of said-one line, said individual markingEQontacts operable in another manner to connectsaid 'test terminals to the test terminalsiorsaiddine in the other finder groups, means for connecting the characteristic marking'for anyone i-of'gsaid other finder groups to said test terminals,-; means for-stopping the movement only of'a finder'of said one other group ona test terminal of {said line, and means for permitting simultaneous {OP- -eration of a finder in each of said finder-groups.

9. A group of finders, a *characteristicemarking for said findergroup, a line having test terminals accessible to-finders of said group and having marking contacts operable for connecting said test terminals to said characteristic-marking, means including said characteristic marking for stopping a finder of said group on'a test terminal-of said line, other groups oi'finders, test terminals for said line'accessible to finders of said other groups, "different characteristi c markings for each of --said othcr groups, s,aid

marking'contactsoperable in case-a finder of said first group is stopped on a tes't'terminal-of said line to; connect the test terminals accessible to finders of said groupto the test terminals-accessible to finders ofsaid-other groups, means for connecting-the characteristic marking-for any one of said other groups to said test'terminals, and means including said last characteristic markingfor stopping only a finderof said-one other ,group- On a test terminal of said line.

JOHN WILLIAM McCL-EW, OWEN AVIS PEARCE; 11

REFERENCES CITED 'Thefollowing references are of recordinthe file of this patent:

UNITED} STATES IJIATENTS H Y Date Number Name. a 1,831,922 McDavltt 'N ov. 1'7, 1931 1,837,801 Vick vDec. 22,;1931

2,278,593 Scheller Apr. 7,- :1942 

